Electric heating unit



C. C. ABBOTT.

ELECTRIC HEATING UNIT,

APPLICATION FILED NOV. 15. 1918.

Patented Feb. 1, 1921,

Inventor: Charfles QfibbOtt, 9 WM His aqttorneg.

UNITED STATES- PATENT OFFICE.

CHARLES C. OF PITTSFIELD. MASSACHUSETTSaA'SSIGNOB TO GHIRRAL ELECTRICCOMPANY. A CORPORATION OF NEW YORK.

ELECTRIC HEATING- UNIT.

i Specification of Lettcrs latent.

Patented Feb. 1. 1921.

Application tiled November is, 1918. Serial No. 262.722.

7 '0 all whom it may concern:

Be itknown that I, CHARLES C. Anno'r'r. a citizen of thel nited States,residing at Pittsfield, county of Berkshire, State of Massachusetts,have invented certain new and useful Improvements in Electric HeatingUnits. of which the following is a specification.

My invention relates to-elctric heating elements of the type in which aresistance conductor is inclosed' in a metallic sheath ducing such aresistance element is to locate a straight resistance conductor. whichmay be called the core wire. centrally of a metallic tube which is toform the sheath and fill the tube with an insulating powder. such asmagnesia. so as to completely embed and properly center the core wire.The ends of the tube are then plugged, suitable provision being made forthe ends of the core wire which extend beyond the tube. and the 'tube issubjected to a reducing process. The result of this operation is thereduction of both the sheath and the core wire, with the consequentcompacting of the insulating material. The arrangement is such that whenthe core wire is reduced to its desired size. the insulating material isso thoroughly compacted that it becomes practically a unit with the corewire and may be drawn or rolled like a solid metal. This element, beingsupplied with the proper terminals, constitutcs an cilicient heatingunit since it is exceedingly rugged and requires no insulat ing support,the core wire being well insulated and protected from mechanical injury.Such a resistance elementnaturally has its limitations. since the spaceavailable for the heating element is not always suflicient to containthe length of conductor necessary to produ e the required resistance;This is particularly true where the element is to be used on a circuitof 220 v. or higher.

I have found that sheath wire having a helical or slllllOlls conductorinstead of a straight core wire may be produced having all theadvantages of the above described .straight conductor sheath wire inaddition to advantages of its own. The principal advantage of this formof unit liesin the fact that a much greater length of core wire may becontained 111 a given. space so that the unit is much more compact andself contained and is readily adapted to *the higher voltages. withoutoccupying increased space. There are other advantages, however, bothfrom the standpoint of the manufacture and of the utility of the unititself which are important. One ofthese advantages arises from the factthat the core wire is not reduced in diameter by the reduction of thesheath. Since the core wire is not drawn down, a of wire which isdifficult to draw. but whlch may be more suitable, may be used. Agreaterthickness' of insulating material which will give greater marginof safety to the electrical insulation may also be used since the corewire is not reduced, whereas in reducing straight core wire, it thethickness of the insulating material is above a certain maximum. thecore wire \vill'not be drawn down properly. Furthermore the core wireretains its surface left by the drawing dies. and a smaller wire may beused than would be safe where it is drawn down in the tube. There arealso certain other advantages. such as simplified terminal connections,greater latitude in thegrade and character of the metals used for thesheath.

In accordance with my invention, therefore, a sinuous or helicalresistance elementis centrally located in a metallic sheath.

filled with powdered insulating material which is compacted to a highdegree so as ,to form a very dense insulating body having relativelyhigh heat conducting properties, so that the heat will be transmitted tothe sheath at the greatest possible rate consistent with good electricalinsulation, there-- by producing a mechanically rugged resistanceelement capable of embodying a high resistance in a relatively smallspace.

My invention will best be understood by reference to the. accompanyingdrawings in which-Figure 1 is a sectional view of the resistanceconductor mounted in a tube ready for filling; Fig. 2 is an end view ofthe same; Fig. 3 is aview of the filled tube partially broken away toshow the terminals; F 1g. 4 is a view showin the unit re duced; and Fig.5 is a detail 0 the terminal- In the manufacture of sheath wire inaccordance with my invention I form a sinuous resistance element whichis preferably in the form of a helix, the material being a highresistance material such as nickelchromium allo This conductor issupported centrally of the tube 11 which may be of any desired metalcapable of being drawn or swaged down. The helix when wound may be aclosed helix but, when it is supported in the tube, it is stretched soas to separate the turns and at the same. time the tension will tend tokeep the helix in a central position. In order to form enlarged tarminals, upon the helix and at the same time furnish a suitable supportfor the helix for 12; as shown in:=detail in Fig; 5.

the filling'and subsequent drawing opera-- tion, I mount each end of thehelix on a rod This rod,

which is preferably of the same material as the core wire, soas toprevent any-galvanic action between the core and the terminals, is

provided with an enlarged upon which the helix fits. wire-is then woundonto the inclined surfacev ofthe head and on to the rod for a plointedhead 13 short distance, theend being finally inserted 5 in a slotMin-the rod. The edges of the slot are then swaged over the end of thewire so as to make a good electrical contact and securely fix the end ofthe wire to'the terminal. The two ends of the helix are thus providedwith terminal sup rts which are passed through holes in tin caps 15 and16 which are fitted over the ends of the tube, the terminals beingsecured to the caps by set screws 17 and 18. The wire is preferablyunder tension, as above inted out, and is supported so that the he ixwill be kept in its proper central position. The cap 15 is provided witha funnel 19 havin rforations 20 throu h which the insu ating material ispou into the tube. The insulating material employed is one which has thequality of compacting into a solid mass and at the same time has highelectrical insulatirig properties and high heat conductivity. agneslumoxid is a suitable material for this purpose. When the tube is filledand the material somewhat compacted by some means, as for instance, byjarring or vibrating the sheath tube, the caps 15 and 16 are removed andthe ends of the tube permanently closed. As shown, this is accomplishedby means of metallic disks 21 and 22 over which the metal is bent, theends of the terminals assin through the disk and being form into heads23 and 24. The tube is'now in the condition shown in Fig. 3. The tube isnow subjected to a reducing process which consists in passin it througha swaging or IOlllng machine. he amount heend ofthe.

'from the spirit of my invention,

of reduction necessary is not great since its purpose is largely tocompact the powdered material around the helix, Ordinarily a reductionin diameter and consequent 13f"!- ening of the tube, such as is represenby the relative dimensions of the parts shown in Figs. and 3, willaccomplish this purpose. I have found, for instance, that a tube havingan outside diameter of g" and an internal diameter of when properlyreduced will have an outside diameter of and an elongation of about 15%.

Que of the results obtained by such a reducing process is that theelectrical resistance of the resistance conductor decreases to a certainextent and this was found to found that there is a direct relationbetween the decreased reslstance and the increase in the length of thetube, that is, the-ratio between the resistance of the helix beforeswagmg and after swagingis equal to the ratio between the length of thetube after swaging and before swa 'ng. The reason i for this seems to bethat since the number of turns of the helix remains the same, while thediameter of the helix is decreased, the

length of each turn is also decreased. The helix is not materiallyextended by drawing it out so asv to se pressing the helix.without-substantial movement of the helix with ref'eiehc'e to thesurrounding insulation. The insulating material is thus verythoroughly'compacted all around the helix. It is, therefore, ssible todetermine very accurately just w at the resistance of the helix will beupon a given reduction, or to put it in another way, it is possible todetermine just when a certain resistance is reached by measuring thelength of the tube. When the tube is properly reduced, the sheath andinsulating material are cut away so as to expose the terminal for somelength, as shown in Fig. 4, and the unit is then ready for use.

While I have described my invention as embodied in concrete form inaccordance with the provisions of the patent statutes, it should beunderstood that I do not limit my Invention thereto, since variousmodifications thereof will suggest themselves to those skilled in theart without departing the scope of which is set forth in the annexedclaims.

What I claim as new and desire to separate the turns but by comeuro byLetters Patent of the United States,

metallic sheath,

insulating material compacted to a hard 2. Ain electric heating unitcomprising a the-sheath to compact the insulating mate- 60 powdered heatrefractory dense mass within saidsheathfand a helix resistance elementembedded in said mass so as ,to readily conduct heat from the resistanceelement to the sheath.

'3. An electric heating unit comprising a metallic sheath,

dense mass within said sheath, a sinuous resistance element embeddedinsaid mass so as to readily conduct heat from. the resist-' anceelement to the sheath and terminal members secured to the'element andprojecting from. the sheath.

4. An electric heating unit comprising a -metallic. sheath, powderedheat refractory -5. .An electric heating unit comprising a metallicsheath,

powdered heat refractory insulating matenalcompacted to a hard densemass within said sheath, a sinuous resistance element embedded in saidmass so as to readily conduct heat from'the res1st-- ance'element to thesheath and terminal members inserted in and secured to the ele ment andhaving reduced end portions profrom the sheath. electric heating unitcomprising a metallic sheatlf, Wdered heat refractory insulating"material compacted to a' hard dense mass within said sheath, a helicalresistance element embedded in said mass so as to readily conduct heatfrom the resistance element to the sheath and terminal members securedto ,the ends of the element and pro- -jecting'from the sheath, saidmembers havmg enlarged ends upon which the element is mo ted. a L

7. The method of forming a resistance unit'which. consists in mounting asinuous resistance elementin a metallic sheath, fillingntihe spacearound the element with a heat re ctosy insulatingmaterial and reducingthe-sheath sufficiently to thoroughly compact the insulating materialaround the resistance element.

8. The method of forming a resistance unit which consists in mounting ahelical resistance elementin a metallic sheath, filling the'space aroundthe element with a heat refractory-insulating material and reducingpowdered heat refractoryinsulating'material compacted to a hard" rialand compress the element without substantially separating its turns.

9. The method'of forming a resistance unit which consists'in securingenlar terminals to. a helical resistance e ement,

"; mounting said element and terminals in a metallic sheath with endsprojecting therefrom and the element under tension filling the spacearound the element with a heat refractory insulating material andreducing the sheath sufiiciently to thoroughly compact the insulatingmaterial around the element and the terminals.

10. The method of'forming an electric heating unit which consists ofmounting a helical resistance element a in a metallic sheath, fillingthe space around the element witha heat refractory insulating materialand then compactingl'the materiaLui-ound the element.

11. The method of forming anv electric heating unit which consists ofmounti a helical resistance element in a-v meta lic compacting thematerial around the element and finally compacting the material stillfurther by reducing the sheath.

12. The method of forming -.an electric heating unit which consists ofmounting a helical resistance element in a metallic sheath, filling thespace around the element with a heat refractory insulating material,

' compact ing the material around the element by a vibrating or jarringaction upon. the material and finally compacting the material still.further by reducing the sheath.

13. The method of forming an electric heating unit which consists infitting terminal members intothe end of a helical resistance conductorand mounting the .same in a metallic sheath, filling the space aroundthe element with a heat refractory insulating material and thencompacting the material around the .element and terminal to fix themagainst displacement. 14. An electric heating unit comprising a metallicsheath, powdered heat refractory insulating, material compacted to ahard dense mass within said sheath, a helical resistance elementembedded in said mass so as to. readily conduct heat from the resistanceelement to the sheath and terminal members inserted in the element andprojecting from the sheath.

In witness whereof, I have, hereunto set my hand this 13th day of Nov.1918.

, CHARLES ABBOTT.

It is hereby certified that in Letters Patent No. 1,367 ,341, grantedFebruary 1,

1921, upon the application of Charles C. Abbott, of Pittsfield,Massachusetts, for

an improvement in Electric Heating Units, an error appears in theprinted specification requiring correction as follows: Page 2, line 76,after the word .of

insert a; and that the said Letters Patent should be read with thiscorrection therein that the same may conform to the record of the casein the Patent Ofliee.

Signed and sealed this 15th day of March, A. D., 1921.

[sun] M. H. couns'ron,

Commissioner qfPatmle. Cl. 219-67.

